Fluorinated polyesters

ABSTRACT

New polyesters comprising polyoxyfluoroalkylene blocks are prepared by polycondensation of diols with dicarboxylic acids or with derivatives thereof, said fluorinated polyesters being characterized by such improved surface properties that any subsequent treatments of the surface of the articles obtained therefrom are needless.

This is a continuation of co-pending application Ser. No. 07/403,071,filed on Sep. 5, 1989, now abandoned, which is a continuationapplication of Ser. No. 07/093,749 filed Jul. 22, 1987, now abandoned.

FIELD OF THE INVENTION

The present invention relates to fluorinated polyesters of thethermoplastic or thermoelastomeric type.

BACKGROUND OF THE INVENTION

There are known thermoplastic polyesters, which are widely utilized asfilms, fibers, supports for magnetic tapes, structural materialsinfields such as the electronic or the biomedical. They are generallyprepared by polycondensation of aromatic diacides or their derivativeswith diols. Typical examples are polyethyleneterephthalate andpolybutyleneterephthalate, which are obtained by polycondensation ofterephthalic acid or a of a derivative thereof, for example a diester,with ethylene glycol or butandiol, respectively.

There are also known thermoelastomeric polyesters obtained bycondensation of a diacid or a derivative thereof, such as e.g. adiester, with a low molecular weight glycol and with a polyglycol,generally a polyoxyalkylene glycol having a molecular weight from 1000to 3000.

The thermoplastic and thermoelastomeric polyesters are characterized byhigh mechanical and electrical characteristics, a good stability tosolvents and to hydrolysis.

For a plurality of uses such as films, supports for magnetic tapes,fibers, in various sectors of goods, they exhibit however considerabledrawbacks, as they have a low oil and water-repellency, a low resistanceto soiling and low free flowing properties, characterized by a highfriction coefficient, so that a subsequent finishing treatment of sucharticles is absolutely necessary.

In particular, as regards the use for magnetic recording tapes, wherethe material flows on metal or plastic surfaces, a surface treatment ofsaid surface with a lubricant is required in order to reduce frictionand to secure the sliding of the tape and preserve it as much aspossible from the wearing. For these uses, very thin layers on thesubstrate surface, generally from 50 to 1,000 Å, are sufficient.

For other uses, for example in particular in the biomedical field, theconventional hydrogenated polyesters, although exhibiting - incomparison with other utilizable materials - improved impermeability andmechanical properties, do not exhibit good biocompatiblity andantithrombogenicity.

With a view to overcoming these drawbacks, the hydrogenated polyestersare therefore subjected to finishing processes or surface treatments.

These finishing processes or these surface treatments are generallycarried out, for example, with a fluorinated diol or with a solution ora dispersion of a fluorinated plastic polymer, such as, for example, apolytetrafluoroethylene dispersion, depending on the type ofapplication. However, these fluorinated coatings exhibit the drawback ofnot sufficiently adhering to the substrate, owing to the surfaceproperties which are typical of the fluorinated polymer and whichinterfere with the adhesion. By consequence, since it is not possible tomaintain the fluorinated layer adherent to the article for asufficiently long period of time, a degradation of the surfaceproperties occurs, such as resistance to chemical agents, oil- andwater-repellency, resistance to soiling, free flowing which, conversely,are indispensable for a plurality of uses.

An alternative method of increasing the duration of the above saidsurface properties consists in chemically binding a fluorinated monomerto the polymeric substrate by grafting. This process can be carried out,for example, by using radiation or electric discharge.

With such method, however, the attainment of a uniform layer is strictlyrelated to the substrate nature. In fact, on substrates having anirregular shape no uniform layer of fluorinated coating can be obtained.

According to another method of obtaining fluorinated coatings onnon-fluorinated polyesters, a non-fluorinated polyester is coextrudedwith a fluorinated copolymer, for example atetrafluoroethylene/hexafluoropropene polymer. This method, however,besides requiring a particularly complex technology, can be rarely used,as it can be applied only for particular types of articles, for examplefibers.

By consequence, there was the requirement of having available readilyprocessable polyesters which permit to overcome the above-said problemsof finishing or of surface treatment, and at the same time having theabove-cited characteristics of chemical inertia, mechanical properties,oil- and water-repellency, biocompatiblity.

THE PRESENT INVENTION

It has now surprisingly been found that polyesters comprisingfluoropolyoxyalkylene units represent a novel technological solutionwhich permits to overcome the above-cited limitations as they permit toavoid all surface treatments or finishing operations.

Thus, the object of the present invention is a polyester characterizedby a block structure and comprising, with respect to the total number ofmoles constituting the polyester, amounts not higher than 45% by molesof at least one fluoropolyoxyalkylene comprising the repeatingfluoropolyoxyalkylene units selected from the following classes:

I (C₂ F₄ O), (CF₂ O), said units being randomly distributed along thefluoropolyoxyalkylene chain;

II (C₃ F₆ O), (C₂ F₄ O), (CFXO) where X=--F or --CF₃, said units beingrandomly distributed along the perfluoropolyoxyalkylene chain;

III --CH₂ --CF₂ --CF₂ --O-- said units being linked to one anotherinside the fluoropolyoxyalkylene chain as shown by the followingstructural formula: --(O--CF₂ --CF₂ --CH₂)_(p) --O--R' _(f) --O--(CH₂--CF₂ --CF₂ --O)_(q) -- where R'_(f) is a fluoroalkylene group,preferably containing 1 to 8 carbon atoms, p and q are integers, p+q isat least 2 and, preferably, up to 200;

IV ##STR1## said units being linked to one another inside thefluoropolyoxyalkylene chain as shown by the following structuralformula: ##STR2## where R_(f) is a fluoroalkylene group, preferablycontaining 1 to 8 carbon atoms, x is 0 or 1, a and b are integers anda+b is at least 2 and, preferably, up to 30;

V (CF₂ CF₂ O);

VI (CF₂ CF₂ CF₂ O).

The fluorinated polyesters of the invention are prepared by directlycarrying out a polycondensation of fluoropolyalkylenes comprising theabove said repeating units with the cited diols or carboxylic diacids orderivatives thereof. Such fluoropolyoxyalkylenes having functionalgroups at both ends contain hydroxy end groups or carboxylic end groupsand have an average molecular weight of from about 400 to 10,000, theminimum value depending on the type of repeating structure, so thatpolyesters having a molecular weight equal to at least 20,000 areobtained.

The polymers so obtained, besides retaining the excellent properties ofthe polyesters, particularly mechanical and electrical properties,chemical inertia to common solvents, exhibit also improved surfacecharacteristics, such as oil- and water-repellency, low frictioncoefficient, chemical inertia to aggressive agents such as hydrocarbonfluids or chlorinated solvents, so avoiding the difficulties connectedwith the preparation and the carrying out of the fluorinated surfacetreatment needed for the conventional polyesters. These materials aretherefore particularly suitable for a wide variety of uses such as e.g.oil- and water-repellent films and fibers, substrates for magnetictapes, biocompatible structural materials for biomedical uss.

For the preparation of the polyesters of the invention the followingcompounds are utilized:

1) a hydrogenated diacid or diester or diacylchloride having thefollowing general formula: ##STR3## wherein Y and Y', equal or differentone another, are halogen or OR', wherein R' is H or an alkyl radicalcontaining from 1 to 8 carbon atoms or an aryl radical having from 6 to10 carbon atoms;

R₂ is a divalent radical having from 2 to 30 carbon atoms such as, forexample:

a) an alkylene radical of the type: ##STR4## wherein m' is an integerfrom 2 to 20; b) a fluorinated or non-fluorinated arylene radical suchas for example para- or meta-phenylene, para- or meta-xylene;

c) a cycloaliphatic or polycyclic, fluorinated or non-fluorinated,divalent radical, such as for example 1,4-cyclohexylene,1,3-cyclohexylene, 2-methyl-1,4-cyclohexylene,2-methyl-1,3-cyclohexylene, diarylenmethane, etc.

Particularly suitable for the purposes of the invention are the aromaticdicarboxylic acids, such as for example the terephthalic, phthalic andisophthalic acids and their derivatives;

2) a hydrogenated diol containing an alkylene radical having from 2 to14 carbon atoms, such as ethylene, propylene, tetremethylene,hexamethylene, dodecmethylene, cyclohexylene, 2,2-dimethyltrimethyleneor cyclohexan-dimethylene;

3) a difunctional derivative having an average molecular weight fromabout 400 to 10,000, preferably from 500 to 5,000, comprising thefluoropolyoxyalkylene units described above in classes I, II, III, IV, Vand VI and having end groups of the following type:

    --(CH.sub.2).sub.v --(CH.sub.2 CH.sub.2).sub.z --A

wherein v and z are integers or zero, preferably v is 0 or 1, and z is 0or an integer up to 3;

A is OH, in such case v being at least 1, or COY, Y being the same asdefined before.

Difunctional derivatives having end groups as described before andbelonging to class I are particularly selected from those comprised inthe following general formula:

    A--(CH.sub.2 CH.sub.2 O).sub.z --(CH.sub.2).sub.v CF.sub.2 O--(C.sub.2 F.sub.4 O).sub.m --(CF.sub.2 O).sub.n --CF.sub.2 --(CH.sub.2).sub.v --(OCH.sub.2 CH.sub.2).sub.z --A

wherein v, z and A have the meaning defined hereinbefore and m and n arepositive integers such that the molecular weight falls within theindicated range.

one can prepare these fluoropolyoxyalkylene derivatives according toknown methods, as described for example in U.S. Pat. No. 3,810,874 andU.S. Pat. No. 3,847,978.

Difunctional derivatives having the above described end groups andbelonging to class II are particularly selected from those comprised infollowing general formula:

    A--CH.sub.2 --CF.sub.2 --(C.sub.3 F.sub.6 O).sub.r (C.sub.2 F.sub.6 O).sub.s (CFXO).sub.t --CF.sub.2 --CH.sub.2 --A

wherein X is --F or --CF₃, indexes r, s, t are positive integers suchthat the molecular weight is as above indicated, and A is as definedhereinbefore.

One can prepare such compounds by photo-oxidation of C₃ F₆ and C₂ F₄mixtures, as described in U.S. Pat. No. 3,665,041, and by successivelyconverting --COF end groups into groups containing the end group A, suchconversion being accomplished according to known methods as describedfor example in U.S. Pat. No. 3,847,978 and U.S. Pat. No. 3,810,874.

Difunctional derivatives having the above described end groups andbelonging to class III are particularly selected from those comprised infollowing general formula:

    A--CF.sub.2 CH.sub.2 (OCF.sub.2 CF.sub.2 CH.sub.2).sub.p --OR'.sub.f O--(CH.sub.2 CF.sub.2 CF.sub.2 O).sub.q CH.sub.2 CF.sub.2 --A

wherein p, q, A and R'_(f) are the same as defined hereinabove.

These compounds are described in published European patent applicationNo. 148,482 and the end groups containing --COF can be converted so asto have end groups A, as is described in U.S. Pat. No. 3,847,978 andU.S. Pat. No. 3,810,874.

Difunctional derivatives having the above described end groups andbelonging to class IV are particularly selected from those comprised infollowing general formula: ##STR5## where a, b, A, R_(f), x have themeaning defined hereinbefore, n is a positive integer.

Such compounds are described in published European patent applicationNo. 151,877 and the end groups containing --COF are converted in orderto have end groups A as is described in U.S. Pat. No. 3,847,978 and U.S.Pat. No. 3,810,874.

Difunctional derivatives having end groups as described before andbelonging to classes V and VI, are prepared by the processes describedrespectively in U.S. Pat. No. 4,523,039 and European patent applicationNo. 148,482, both successively followed by the treatments described inItalian patent application No. 22920 A/85;

4) a hydrogenated polyoxyalkylene glycol having an average molecularweight from about 400 to 4,000 and preferably from 1,000 to 2,000,having the following general formula:

    HO(C.sub.d H.sub.2d O).sub.g H

where d=1-4 and g=6-70, C_(d) H_(2d) being linear or having side-chains.

Representative examples of such class of compounds are: polyethyleneglycol, polypropylene glycol, polytetramethylene glycol.

The fluorinated polyester of the present invention are prepared byproperly mixing the above-specified compounds in such way that at leastone of them is a fluoropolyoxyalkylene derivative and the molecularweight of the final polyester is not lower than 20,000.

According to the present invention, the fluorinated polyesterscomprising the fluoropolyoxyalkylene derivative in amounts not exceeding5% by moles, preferably from 0.1% to 5% by moles with respect to thetotal number of moles consisting the polyester are particularly suitablefor substrates for magnetic tapes, oil- and water-repellent films andfibers.

The polyesters of the invention having a content offluoropolyoxyalkylene units higher than 5% by moles are particularlyutilizable in the biomedical field due to their high biocompatiblity.

By properly varying the components from 1) to 4), it is possible toobtain thermoplastic or thermoplastic materials. The thermoelastomericmaterials contain a rubber-like phase which may consist either offluoropolyoxyalkylene or of polyoxyalkylene glycol or of mixturesthereof. Generally, in the presence of high fluoropolyoxyalkylenecontents, for example of 30% by moles, the polyester isthermoelastomeric; in case of lower amounts, ≦5% by moles, it isnecessary to add polyoxyalkylene glycols.

One can prepare the polyesters of the invention by conventionalpolycondensation techniques, such as for example, in bulk, in solution,in emulsion, interface polycondensation.

Always according to the known polyester synthesis methods, thepolycondensation can be carried out starting from dicarboxylic acids anddiols, or by transesterification starting from diesters and diols, orfrom diacylchlorides and diols.

Particularly suitable for the purposes of the present invention is thetransesterification and bulk-polycondensation process starring frommixtures of diesters and diols.

Such process is accomplished by first heating the mixture of reagentsdiesters and diols, in proper molar ratios, in the presence of acatalyst, to a temperature from about 200° C. to 240° C.; in this step,the distillation of the by-products (alcohols) generated during thetransesterification takes place.

The reaction is carried out in an inert atmosphere, under vigorousstirring and for a time sufficient for the complete removal of theby-products.

The operation time depends on the monomer type, the temperature, thecatalyst and the excess of diol employed.

This process step leads to a low molecular weight prepolymer which isconverted to a polymer having a molecular weight suitable for hightemperature (250° C.-300° C.) polycondensation under stirring and at aresidual pressure lower than 1 torr, in order to remove the excess ofthe low molecular weight diol.

The polycondensation time, which is a function of the operativeconditions, generally ranges from 0.5 to 10 hours.

It is possible to use different types of catalysts, such as, forexample, salts of divalent and trivalent metals, such as calcium,manganese, iron, magnesium, aluminum, zinc; oxides of germanium, leadand antimony; alkaline metals (sodium, potassium) alkoxides, titaniumalkoxides (isopropylate, butylate).

Both process steps, i.e. transesterification and polycondensation, aregenerally effected in the absence of solvents: the materials are in themolten state.

The polycondensation can be also carried out in solution, usingdiacylchlorides and diols.

The fluorinated polyesters of the present invention, as mentioned above,permit to obtain, by suitably varying the starring composition of themixture, both plastic-type and elastomeric-type materials, each typebeing characterized by excellent mechanical properties. Those skilled inthe art will have no difficulty in determining the best compositions forthe various utilizations.

The mechanical properties of these fluorinated polyesters, however, canbe modified, according to the requirements and the desired appliances,by adding various inorganic additives known in the art, such as carbonblack, silica gel, alumina and glass fibers. For a few uses, inparticular, it is advisable to incorporate stabilizers to heat and toultraviolet radiations, well known in the art.

Furthermore, it is possible to obtain polyesters with a differentfluorine content by properly varying the initial molar ratio of thefluoropolyoxyalkylene derivative to other reagents.

The fluorinated polyesters obtained according to the present inventionhave the same fields of use as the analogous non-fluorinated polyesterswith the advantage that the articles prepared from said fluorinatedpolyesters, for example, by injection molding or compression moldingprocesses, exhibit, as compared with the known products, improvedproperties as regards oil- and water-repellency, self-lubrication, freeflowing and biocompatiblity.

This properties improvement occurs also for very low amounts, even of0.5% by moles, of fluoropolyoxyalkylene compound with respect to thefinal polyester.

A further advantage of the polyesters of the present invention is thepossibility of mixing a thermoplastic or thermoelastomeric polyesterhaving a high fluorine content, according to the invention, with otherfluorinated or non-fluorinated polymeric materials, and of treating theresulting mixture according to a suitable conversion technology. In thisway it is possible to have available a wide range of materials endowedwith improved properties in comparison with those obtained from theindividual components of the mixtures.

The polyesters of the invention were characterized by determining:

    ______________________________________                                        Melting point:  thermal differential analysis at a                                            heating rate of 20° C./minute.                         Technological properties:                                                     modulus         ASTM D 638 and D 412                                          tensile strength                                                              elongation at break                                                           Shore hardness  ASTM D 2240                                                   contact angle:  determination by means of a 40 X                                              grazing light microscope                                      friction coefficient                                                                          ASTM D 1894-73                                                water absorption                                                                              ASTM D 570 - 24 hours.                                        ______________________________________                                    

The test-pieces were prepared by compression molding, operating attemperature higher 30° C.-40° C. than the polymer melting point, thepolymer having been previously dried at 100° C. under vacuum.

EXAMPLES

The following examples are given for merely illustrative purposes andare not to be considered as limitative of the invention.

EXAMPLE 1

120.6 g (0.62 mols) of dimethyl terephthalate (DMT), 89.4 g (0.99 mols)of 1,4-butandiol and 1.2 10⁻³ mols of titanium tetraisopropylate (in anisopropanol solution) were charged into a tree-neck flash having a0.5-liter volume, equipped with a stirrer, a dropping funnel and acolumn for the distillation of the reaction by-products.

Into the dropping funnel there were introduced 62 g (0.031 mols) ofα,ω-bis-hydroxy-polyoxyperfluoroalkylene having an average molecularweight equal to 2000 (formula described at point 3), belonging to classI with A=OH; v=1; z=1).

The flask was repeatedly subjected to vacuum and nitrogen-filling cyclesand was subsequently dipped into an oil bath previously heated to 200°C.

The reaction was conducted under stirring and in a nitrogen atmosphere,and the methanol distillation begun directly after melting of the mass.

After 30 minutes, when the distillation of the theoretical amount ofmethanol was concluded, the polyoxyperfluoroalkylene diol was added andthe whole was allowed to react for 1 hour at 210° C.

The bath temperature was then brought to 250° C. while the pressure wasgradually lowered to 0.1 torr.

Polycondensation was carried out for 2 hours, where-after it was cooledto room temperature while simultaneously introducing nitrogen into thereaction flask until the atmospheric pressure was reached.

The fluorinated polyester, having the appearance of a light mass,exhibited the following characteristics:

melting point: 220° C.

Fluorine content: 18% by weight

Shore hardness D: 72

tensile strength: 540 kg/cm²

elongation at break: 310%.

The oil- and water-repellency properties and the friction coefficient ofthe fluorinated polyester were compared with those of apolybutyleneterephthalate sample (check A).

    ______________________________________                                                          Fluorinated                                                                   polyester                                                                             Check A                                             ______________________________________                                        contact angle with H.sub.2 O                                                                      104       55                                              contact angle with ligroin                                                                        20        complete                                                                      wetting                                         contact angle with nitromethane                                                                   55        36                                              dynamic friction coefficient (μ)                                                                  0.15      0.33                                         on steel                                                                      H.sub.2 O absorption (% by weight)                                                                   0.08      0.65                                         ______________________________________                                    

EXAMPLE 1

Using the apparatus and the modalities described in example 1, afluorinated thermoelastomeric polyester was prepared, which consisted ofa rigid crystalline phase, a rubber-like amorphous hydrogenated phase,an amorphous fluorinated phase having a very low Tg.

The reaction mass consisted of DMT (48.5 g, equal to 0.25 mols),1,4-butandiol (36 g, equal to 0.04 mols), polyoxytetramethylene glycolhaving an average molecular weight equal to 1000 (100 g equal to 0.1mols) and Irganox 1098® (1 g) as antioxidant. In the second step therewas added α,ω-bis-hydroxy-polyoxyperfluoroalkylene having an averagemolecular weight equal to 2000 and having the formula described at point3), belonging to class I with A=OH; v=1; z=1 (12.5 g corresponding to0.00625 moles). The catalyst is titanium tetraisopropylate (0.1% bymoles referred to DMT).

After a 2-hours polycondensation, a high molecular weight fluorinatedcopolyester was obtained, exhibited the following properties:

melting point: 194° C.

Fluorine content: 4.6% by weight

Shore hardness D: 52

tensile yield strength (25% modulus): 132 kg/cm²

tensile strength: 490 kg/cm²

elongation at break: 480%.

Analogously with the preceding example, the fluorinated polymerproperties were compared with those of a thermoelastomericcopolyether-ester not containing fluorine (check B).

    ______________________________________                                                        Fluorinated                                                                   thermoelastomeric                                                             polyester   Check B                                           ______________________________________                                        contact angle with H.sub.2 O                                                                    110           62                                            contact angle with ligroin                                                                      15            complete                                                                      wetting                                       contact angle with nitromethane                                                                 59            39                                            dynamic friction coefficient (μ)                                                                0.20          0.45                                       on steel                                                                      ______________________________________                                    

EXAMPLE 3

776 g (4 mols) of dimethylterephthalate, 744 g (12 mols) of ethyleneglycol, 0.7 g of manganese acetate (II) and 0.7 g of antimony oxide(III) were charged into a glass reactor having a 3 1 volume, equippedwith a stirrer, a dropping funnel and a column for the distillation ofthe reaction by-products.

Into the dropping funnel there were introduced 80 g (0.04 mols) ofα,ω-bis-(methylcarboxylate)-polyoxyperfluoroalkylene having an averagemolecular weight equal to 2000 (formula described at point 3), belongingto class I, with A=COOCH₃, v=z 0).

The reactor was repeatedly subjected to vacuum cycles and wassubsequently dipped into an oil bath heated to 180° C.

The mixture was stirred for 2 hours, during which the distillation ofmethanol toke place; after this period of time, the fluorinated diesterwas added and the whole was allowed to further react for 1 hour.

The bath temperature was then brought to 280° C. while simultaneouslyand progressively reducing the pressure to 0.1 mm Hg.

After a 2-hour polycondensation, during which the distillation of theethylene glycol in excess occurred, it was cooled to room temperature.

The fluorinated polyester, (m.p.=250° C., Fluorine content=5% byweight), after grinding in rotary ball mill, was extruded at 290° C. bymeans of a laboratory flat-head extruder, was cooled to 25° C.,longitudinally stretched at 95° C. to 300%, transversely stretched at120°0 C. to 300% and subsequently treated at 215° C. for a few secondsto give a biaxially oriented film having a thickness of 100 μm.

The fluorinated polyester film exhibited improved surface propertieswith respect to a conventional polybutyleneterephthalate film.

In fact, the values of the contact angle with H₂ O and of the dynamicfriction coefficient on steel were equal to 103° and to 0.25,respectively, in comparison with 70° and 0.55 of apolybutyleneterephthalate film not containing fluorine.

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims. The above references are hereby incorporated byreference.

We claim:
 1. A polyester having a block structure prepared throughpolycondensation reaction of the following compounds:A) a hydrogenateddiacid or diester or diacylchloride having the following generalformula: ##STR6## wherein Y and Y', equal to or different from eachother, are halogen or OR', wherein R' is H or an alkyl radical havingfrom 1 to 8 carbon atoms or an aryl radical having from 6 to 10 carbonatoms; R₂ is a divalent radical having from 2 to 30 carbon atoms,selected from the class consisting of:i) an alkylene radical; ii) afluorinated or non-fluorinated arylene radical; iii) a cycloaliphatic orpolycyclic, fluorinated or non-fluorinated, divalent radical; B) ahydrogenated diol containing an alkylene radical having from 2 to 14carbon atoms,; C) a difunctional fluorinated compound having an averagemolecular weight from about 400 to 10,000, consisting of sequences offluoropolyoxyalkylene units and having end groups of the following type:

    --(CH.sub.2).sub.v --(OCH.sub.2 CH.sub.2).sub.z --A

wherein v and z are integers or zero, A is OH, in such case v being atleast 1, or COY, Y being as defined hereinbefore at time A), said fluorooxyalkylene units being selected from the following classes:I) (C₂ F₄O), (CF₂ O), said units being randomly distributed along thefluoropolyoxyalkylene chain; II) (C₃ F₆ O), (C₂ F₄ O), (CFXO) with S=--For --CF₃, said units being randomly distributed along thefluoropolyoxyalkylene china; III) --CH₂ --CF₂ -13 CF₂ --O said unitsbeing linked to one another inside the fluoroalkylene chain as shown bythe following structural formula:

    --(O--CF.sub.2 --CF.sub.2 --CH.sub.2).sub.p --O--R'.sub.f --O--(CH.sub.2 CF.sub.2 CF.sub.2 O).sub.q --

where R'_(f) is a fluoroalkylene group, p and are integers, and p+q isat least 2; IV) ##STR7## said units being linked to one another insidethe fluoropolyoxyalkylene chain as shown by the following structuralformula: ##STR8## wherein R_(f) is a fluoroalkylene group, x is 0 or 1,a and b are integers, and a+b is at least 2; V) (CF₂ CF₂ O); and VI)(CF₂ CF₂ CF₂ O); said polyester being furthermore characterized in thatthe fluorinated compound of item C) is present in the final polyesterproduction amount from 0.2% to 2.0% by moles based on the total moles ofA)+B)+C).
 2. Polyester according to claim 1, wherein in thepolycondensation reaction is used also a hydrogenated polyoxyalkyleneglycol having an average molecular weight from about 400 to 4,000,having the following general formula:

    HO(C.sub.d H.sub.2d O).sub.g H

where d=1-4 and g=6-70, C_(d) H_(d) being linear or having side chains.3. The polyester according to claim 1, wherein the alkylene radical ofitem i) is selected from the class consisting of ##STR9## where m' is aninteger from 2 to
 20. 4. The polyester according to claim 1, wherein thearylene radical of item ii) is selected from the class consisting ofpara-phenylene, meta-phenylene, para-xylene, and meta-xylene.
 5. Thepolyester according to claim 1, wherein the divalent radical of itemiii) is selected from the class consisting of 1,4-cyclo-hexylene,1,3-cyclohexylene, 2-methyl-1,4-cyclohexylene,2-methyl-1,3-cyclohexylene, and darylemenmethane.
 6. The polyesteraccording to claim 1, wherein the difunctional fluorinated compound C)has an average molecular width from 500 to 5,000.
 7. The polyesteraccording to claim 2, wherein the polyoxyalkylene glycol has an averagemolecular width from 1,000 to 2,000.
 8. The polyester according to claim1, wherein v is zero or 1 and z is zero or an integer from 1 to
 3. 9.The polyester according to claim 1, wherein the difunctional fluorinatedcompound C) is an aromatic dicarboxylic acid.
 10. The polyesteraccording to claim 1, wherein the difunctional fluorinated compound C)has the following formula:A--(CH₂ CH₂ O)_(z) --(CH₂)_(v) --CF₂ O--(C₂ F₄O)_(m) --(CF₂ O)--CF₂ --(CH₂)_(v) --(OCH₂ CH₂)_(z) --Awherein v, z and Ahave the same meaning as defined in claim 16 and m and n are positiveintegers such that the molecular weight falls within the range400-10,000.